(a) Field of the Invention
The present invention relates to a probe pin for a probe card and, more particularly, to a probe pin of a probe card for use in testing electric characteristics of a semiconductor circuit or LSI.
(b) Description of the Related Art
Semiconductor circuits fabricated as semiconductor chips on a semiconductor wafer are generally subjected to a product test for electric characteristics thereof by using a probe card and a circuit tester before separating the wafer into a plurality separate chips.
FIG. 1 shows a typical probe card for use in testing a semiconductor chip. The probe card, generally designated by numeral 10, includes a card plate 14 having therein a central aperture 12, and a large number of probe pins attached onto the outer peripheral area of the bottom surface of the card plate 14 and extending downward in a slanting direction from the peripheral area toward the central aperture 12 of the card plate 14. The tip of each probe pin 16 is located right under the central aperture 12.
The base of each probe pin 16 is in contact with the bottom of a via plug 22 penetrating the card plate 14, and is connected to a card terminal 28 through the via plug and an interconnect wire 26. The card terminal 28 is electrically connected to a circuit tester not shown. The probe pin 16 has a tip portion directed substantially in the vertical direction, and is supported in the vicinity of the tip portion by a pin support 24 made of epoxy resin and formed on the card plate 14 in the vicinity of the periphery of the central aperture 12. A semiconductor chip is generally tested by the probe card 10 while the tip of the probe pin 16 slides on a chip electrode 18 of the semiconductor chip under test in a semiconductor wafer 20.
The probe pin 16 is made of a hard metal, such as tungsten (W), rhenium-containing tungsten (ReW), beryllium copper (BeCu) etc., having a superior workability and an excellent elasticity. For manufacture of the probe pin 16, an ingot of the hard metal is subjected to extension to form a small-diameter metallic wire having a circular cross-section. ReW is most suited for the material of the probe pin 16 due to its large elasticity, superior resistance against abrasion, and superior workability or a property suitably formed into a metallic wire having a diameter of several tens of micrometers.
Although it is known that ReW is most suited for the material of the probe pin for the present, as described above, there is a disadvantage in that ReW is liable to oxidation on the surface thereof. For example, ReW left in an oxidation ambient for a single day is oxidized on the surface thereof to be coated with an oxide film having a higher electric resistance, which raises the contact resistance between the probe pin and the chip electrode.
In addition, since the chip electrode to be contacted by the probe pin is generally made of aluminum which is also liable to oxidation. The tip of the probe pin, after repeated contacts with the chip electrodes, is attached with aluminum powder, which is oxidized to coat the tip of the probe pin with an aluminum oxide film. This also raises the contact resistance.
For solving the above problem, the tip of the probe pin is ground or polished using a grinding or polishing tool each time after the probe pin is used for testing several tens or several hundreds of semiconductor chips. The grinding by tool raises the cost and time for the testing.
Patent Publication JP-A-11-38039 describes a probe pin having a metallic body coated with a non-oxidizable metallic film after shaping the metallic body. The non-oxidizable metallic film is formed on the metallic body made of tungsten by metallization to a thickness of several micrometers, followed by a heat treatment in a vacuum ambient or non-oxidizing ambient to diffuse non-oxidizable metal from the non-oxidizable metallic film to the tungsten body, thereby improving the resistance of the tungsten body against oxidation. A plurality of resultant probe pins are then attached and fixed onto a card plate, followed by grinding the tips of the probe pins to have a uniform height with respect to the bottom of the card plate.
The probe pin described in the above publication, however, has the following disadvantages:
(1) tungsten is also diffused from the tungsten body to the non-oxidizable metallic film by a metallic solid diffusion during the heat treatment, whereby the surface of the probe pin changes the state thereof;
(2) a poor adherence between the tungsten body and the non-oxidizable metallic film is likely to cause a peel-off therebetween;
(3) although the adherence may be improved by polishing the surface of the tungsten body for smoothing or by forming the metallic film to have a larger thickness, it raises the cost of the probe card; and
(4) the non-oxidizable metallic film is likely to be removed by the grinding of the tips of the probe pins for a uniform height.
In view of the above problems in the conventional technique, it is an object of the present invention to provide a probe pin having a lower contact resistance with the chip electrode without polishing or grinding the tip thereof after repeated contact with the chip electrodes. The present invention also relates to a probe card having such probe pins and a method for manufacturing the probe card.
The present invention provides, in one aspect thereof, a probe pin for use in a probe card including a metallic body, a nickel plating film formed on the metallic body, and a non-oxidizable film made of at least one of platinum group metals formed on the nickel plating film.
The present invention provides, in another aspect thereof, a probe card including a card plate and a plurality of probe pins fixed onto the card plate, each of the probe pins including a metallic body, a nickel plating film formed on the metallic body, and a non-oxidizable film made of at least one of platinum group metals formed on the nickel plating film.
The present invention provides, in another aspect thereof, a method for fabricating a probe card including the steps of: forming a plurality of metallic bodies by taper-shaping and bending metallic wires; fixing the metallic bodies to a card plate, polishing tips of the metallic bodies fixed onto the card plate so that the metallic bodies have a substantially uniform height with respect to a surface of the card plate; and plating the probe bodies fixed onto the card plate to form consecutively a nickel plating film and a non-oxidizable metallic film on the metallic bodies.
In accordance with the probe pin and the probe card of the present invention and the probe card manufactured by the method of the present invention, the nickel plating film functions as a smoothing underlying layer for improving the adherence between the metallic body and the overlying non-oxidizable metallic film and as a barrier layer for preventing the metallic solid diffusion between the metal of the metallic body and the metal of the non-oxidizable metallic film. The nickel plating film has an anchor function wherein nickel in the nickel plating film enters the depressions on the surface of the metallic body, thereby having an excellent adherence with respect to the metallic body.
The smooth surface of the nickel plating film also affords a smooth surface for the non-oxidizable metallic film, thereby preventing attachment of aluminum powder onto the non-oxidizable metallic film from the chip electrode. Thus, the tip of the probe pin is substantially free from oxidation after a larger number of repeated contacts with the chip electrodes of semiconductor chips without polishing the tip of the probe pin.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.